Material Selection Guidelines for Geothermal Power Systems—An Overview

Abstract

Perhaps the most important difference between traditional electric power generation and geothermal power generation is the potentially severe corrosion of metals caused by the use of the geothermal fluids. The object of this overview is to present the principal results of work conducted for the U.S. Department of Energy under Contract EG-77-C-04-3904. Process streams are identified by the presentation of nine geothermal power cycles applicable to four types of liquid-dominated geothermal resources found in the United States. Of the many constituents in geothermal fluids, seven key chemical species are identified that account for most corrosion phenomena in geothermal power systems. These species are: oxygen, hydrogen sulfide, carbon dioxide, ammonia, chloride, sulfate, and hydrogen ion concentrations. Based on analyses of actual geothermal materials test data and test methods, the performance of metals in geothermal fluid, steam, and condensate is presented for carbon and stainless steels, titanium, nickel, copper, and many other alloys. The applicability of new nonmetallic materials in geothermal systems is also addressed. Finally, the similarities and differences between seawater and geothermal corrosion phenomena are discussed.